The uses of ion-conducting materials in electrochemical applications such as fuel cells, dialysis cells, electrolysis cells and electrochemical separation methods, are limited by their hydrolytic and thermo-oxidative stability zones, which are often within a range below 100° C. However, for a number of applications, such as in the case of the fuel cell, it is advantageous to achieve higher working temperatures (approx. 100-200° C.). On the one hand, this requires less cooling for the fuel cell; on the other hand, the electric performance of the cell increases with higher temperatures, due to accelerated electrode reactions and reduced electrode contamination (e.g. due to CO from a reformer).
Higher temperatures, particularly in a water- and oxygen-containing environment, require chemically, thermally, thermo-oxidatively and hydrolytically stable materials.
At the moment, essentially perfluorated sulfonated polymers (e.g. Nafion®) are used, for example, in the area of fuel cell technology; these generally have a high chemical, thermal and thermo-oxidative stability, but are expensive and time-consuming in their manufacture and disposal. A more cost-effective alternative to perfluorated polymers is presented by membrane materials based on sulfonated poly(arylenes), such as poly(arylene ether ketones), poly(arylene ether sulfones) and poly(arylene thioether sulfones), which are currently being tested for fuel cells. (General references on the state of the art of fuel cells and suitable membrane materials, as well as the synthesis of the above-mentioned and other poly(arylenes), are indicated in the literature overview on page 78-81 of the application text).
In terms of structure, poly(arylene ether ketones), poly(arylene ether sulfones) and poly(arylene thioether sulfones) share the characteristic that at least one electron-donor bridge group (such as ether —O— or thio —S—) is bound to the sulfonated aromatic ring. Since the hydrolytic stability of the sulfonic acid group at the aromatic ring is impaired by electron-donor substituents (such as ether —O— or thio —S—), these polymers tend towards decomposition reactions in the sulfonic acid group at higher temperatures. Furthermore, ether bridges in particular are not sufficiently resistant to oxidative attacks (such as peroxide radicals, Fenton's test).
Therefore, it could be helpful to provide new hydrolytically and thermo-oxidatively stable polymers that may be used advantageously, particularly for membrane and fuel cell technologies, and can be produced in a cost-effective manner, as well as providing methods for producing such polymers.